Immunotherapy improves survival in advanced prostate cancer

Sipuleucel-T represents the “first active immunotherapy to demonstrate improvement in overall survival for advanced prostate cancer,” said David Penson, MD, MPH, who announced the results of a phase 3 study known as Immunotherapy for Prostate Adenocarcinoma Treatment (IMPACT), at the American Urological Association (AUA) 2009 Annual Meeting.

The prostate cancer vaccine “has the potential to create a new treatment paradigm in oncology,” said Dr Penson, professor of urology at the University of Southern California, Los Angeles.

Sipuleucel-T is an autologous active cellular immunotherapy that activates the immune system against prostate cancer.

In the study, 512 men with minimally symptomatic, metastatic, castrate-resistant prostate cancer were randomized to receive the vaccine or placebo in a 2:1 ratio. “This is a pretty desperate group that has a median survival of less than 2 years,” he said.

The complete course of therapy is delivered in 3 sessions at 2-week intervals. For each session, the patient goes to an apheresis center for leukapheresis to harvest dendritic cells on Day 1, the vaccine is manufactured on Days 2/3 by attaching the dendritic cells to prostatic acid phosphatase (PAP), and the patient is infused with the dendritic cells labeled with PAP on the next day. Docetaxel could be added to the treatment regimen if patients had radiographic progression of disease.

In an intent-to-treat (ITT) analysis, the median survival was 25.8 months in men randomized to sipuleucel-T and 21.7 months in those randomized to placebo, for a median survival benefit of 4.1 months (HR=0.775; P=.032). Three-year survival was improved by 38% in the immunotherapy arm. The relative survival benefit with immunotherapy was maintained across multiple sensitivity analyses.

The time to objective disease progression was not altered significantly in the immunotherapy recipients, but this end point is difficult to measure reliably and does not correlate with survival, said Dr Penson.

Chills occurred in 54.1% of the vaccine recipients versus 12.5% of theplacebo recipients. Pyrexia, headache, a brief influenza-like illness, hypertension, and hyperhidrosis were also more common in the vaccine group.

The rate of any serious adverse event was not significantly different between the 2 groups (24% with sipuleucel-T vs 23.8% with placebo).

The relative survival benefit associated with the vaccine was consistent across all three phase 3 studies conducted with sipuleucel-T, said Dr Penson.

The short duration of therapy, as opposed to the 3 to 4 months required for chemotherapy, and the minimal side effects observed with this agent create a highly favorable benefit:risk ratio for sipuleucel-T, Dr Penson said.